The present invention relates to an onsite method and apparatus for treating contaminated drill cuttings before disposal and more particularly relates to a method and means for removing oil or like contaminants from drill cuttings at a drilling site, e.g., an offshore location, before final disposition of the cuttings, e.g., dumping the cuttings into the water at an offshore site.
In a rotary drilling operation, a fluid commonly called "mud" is circulated from a storage area on the surface, downward through the drill pipe, out openings in the drill bit, and upward within the borehole to the surface. This return mud carries with it the drill cuttings from the bottom of the borehole. The returning mud along with its entrained drill cuttings is passed onto a "shale shaker" before it is returned to the storage area. The shaker, which normally sits above the mud storage area, is essentially a screen that is used to separate the drill cuttings and cavings from the mud. The mud falls by gravity through the screen and the cuttings pass over the end of the screen.
Disposal of these separated cuttings is sometimes a real problem, e.g., where the drilling operations are carried out at an offshore location. In some instances, the cuttings are passed from the shaker back into the water and are allowed to settle to the bottom. However, as is often the case, when a drilling mud system such as an oil-base mud is used which coats the cuttings with undesirable contaminants, e.g., oil, the cuttings cannot be disposed of directly into the water without the risk of polluting the area around the drilling site. Although the disposal of contaminated drill cuttings is complicated at an offshore location, it may also be a major problem at onshore locations where ecological considerations prevent the normal disposal of untreated cuttings.
There are two general techniques for treating these contaminated cuttings to make them ecologically acceptable. Either they must be hauled or barged to disposal facilities on shore or they must be treated on site to remove the contaminants before they are disposed of in the water. The added expense involved in hauling the cuttings ashore is substantial, and, accordingly, seriously detracts from widespread commercial application of this technique. Further, the technique of hauling of the cuttings to shore for disposal may be impractical in areas of bad weather and rough seas. Therefore, for obvious reasons, it is much preferred to treat and dispose of the drill cuttings from offshore operations directly at the drilling site.
To treat contaminated cuttings onsite, at least two different types of methods have been proposed. One approach is to burn oil off the cuttings with high intensity lamps. However, this approach presents problems (i.e., possible fire hazards due to the lamps and the difficulty of equally exposing all the cuttings to the lamps) which makes it unfeasible in most instances.
The second approach involved washing the cuttings with a detergent to remove the contaminants, separating the washing solution and contaminants, and dumping the cleaned cuttings into the water. One example of this approach is disclosed in U.S. Pat. No. 3,688,781, issued Sept. 5, 1972. Other wash techniques are discussed in the article "Cuttings Can Meet Offshore Environment Specifications", OIL AND GAS JOURNAL, Aug. 14, 1972, pp. 73-76. While such techniques may be successful in cleaning the cuttings, there still exists a possibility that some pollution may result if the detergent, itself, is not properly handled.